1. Field of Invention
This invention pertains to a device for measuring accurately a linear dimension of an object and more particularly to a device used for determining whether said linear dimension is within a preselected range or tolerance. The present invention further relates to a method of measuring a linear dimension of an object, such as the width of a metal strip.
2. Description of the Prior Art
The subject device is directed to the art of measuring a linear dimension of objects such as wide, relatively thin metal strips. Typically such strips are made by slitting a metal sheet into strips of selected nominal widths. Normally the tolerances for these dimensions are related to the actual widths of the strips. For example a typical tolerance for a strip of 0.5" to 3" is .+-.0.005" while for a wider strip in the range of 9-18" the tolerance may be .+-.0.010 to .+-.0.016". The width of strips can be measured to determine whether these tolerances are met by using existing micrometers or calipers. However in some instances there is a need for relatively wide strips made to much closer tolerances usually associated with the thin strips. Thus for example in some instances a strip in the range of 9-18" may be required having a tolerance of +0.005". However it is very difficult to determine whether a wide strip has this narrow tolerance with present instruments and measurement techniques. For instance measurement errors can occur if the strip is not measured exactly perpendicularly across its sides or if the measurement instrument has edges which are not positioned parallel to the edges of the strip. In this situation the true width is not the actual width but is equal to the product of the measured dimension and the cosine of the measurement angle. Finally, the measurement is also adversely affected if the strip is held by hand since it is relatively flexible and may bend during the measuring step.
In view of the above-mentioned disadvantages, it is apparent that there is a need for a better device and method for measuring the linear dimension of an object accurately.